A color picture tube includes an electron gun for generating and directing three electron beams to a screen of the tube. The screen is located on the inner surface of a faceplate of the tube and comprises an array of elements of three different color emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen, to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube faceplate. A focus mask comprises dual sets of conductive lines that are perpendicular to each other and usually separated by an insulative layer.
U.S. Pat. No. 5,646,478, issued to R. W. Nosker et al. on Jul. 8, 1997, and U.S. Pat. No. 5,647,653, issued to S. C. Cherukuri on Jul. 15, 1997, disclose focus mask tubes wherein the masks are formed by two perpendicular sets of metal strands. One set of strands is under tension and includes an insulator coating that is applied in two layers of different materials. The second or top layer is used to attach the second set of strands to the first set, by sintering. U.S. Pat. No. 5,629,051, issued to E. S. Poliniak on May 13, 1997, discloses a method of applying the insulator coating to the first set of strands.
A few problems exist with the technique of attaching the two sets of strands. For example, the second insulator layer can chip, thereby leaving particles within a tube. When subjected to shock, the strands may shift relative to each other, and, because of their mutual attachment, the strands may be unable to return to their original positions. The present invention provides a mask structure that eliminates such problems.